In the months since the Prudential Insurance Company agreed to pay at least $410 million to settle claims by policyholders that they had been deceived by sales agents, the company has quietly begun a legal fight to keep documents from customers who rejected the settlement.

In early spring, Prudential won court rulings in Florida and New Jersey to keep documents secret. In recent weeks, its campaign has prevailed in Texas. The proceedings in New Jersey, conducted in Federal District Court here, were themselves held in secret from late March until late June after a Federal magistrate ordered the proceedings and all of their records sealed at Prudential's request.

Lawyers for the disgruntled policyholders who have refused to participate in the national class action settlement, reached in March, say that they believe the documents contain valuable evidence supporting their clients' claims that agents misrepresented the true costs of new life insurance policies from 1982 to 1995 and that they are now entitled to punitive damages from the Newark-based insurer.

Although the settlement could ultimately cost Prudential up to $1 billion, customers who chose to participate in it are generally expected to receive as much as $3,100 each, lawyers who worked on the settlement have said. But those now seeking punitive damages hope to win far larger awards. A. Anderson B. Dogali, a lawyer in Florida representing 105 of those policyholders, said it was impossible to predict the amounts juries might award them. But he noted that juries in Alabama in 1994 and 1995 ordered Prudential to pay $50 million in punitive damages in two lawsuits charging deceptive sales.

Prudential challenged both awards as ''grossly excessive,'' and reached agreements with the policyholders to pay less. Robert DeFillippo, a Prudential spokesman, refused last week to reveal the amounts.

The insurance company's legal fight centers on a box of about 65 documents now held by the Florida Insurance Department. The documents contain some records that the state relied on last February when it fined Prudential $15 million for deceptive sales practices.

Prudential contends that the Florida documents are confidential company records protected by attorney-client privilege. The company says that they were stolen by a high-ranking Prudential lawyer and that outsiders, including state governments, cannot legally possess them or share them with the public. Mr. DeFillippo declined to discuss the documents' contents, although in court papers filed in March in Federal court here, the company argued that lawyers for the policyholders could use the documents in their lawsuits, causing the company ''substantial and irreparable harm.''

With their investigations of Prudential complete, Florida's Insurance Department and Attorney General's office want to turn over the documents to anyone interested in them, under the state's liberal open-records law.

But Judge Charles McClure of the Florida Circuit Court sided in April with a Prudential objection to disclosure and issued an injunction barring the policyholders' lawyers, or any member of the public, from inspecting them. They remain far from the public domain, tucked in a box under the desk of Douglas Shropshire, a senior lawyer in the Florida Insurance Department and head of its investigation of Prudential.

Mr. Dogali says he is frustrated and convinced that Prudential ''will spare no expense'' to shield the documents.

''The material Prudential is going to great length to conceal, I believe, contains strong evidence of fraud that would be very valuable to policyholder-plaintiffs,'' Mr. Dogali said. ''Prudential's effort to conceal them, standing alone, is meaningful.''

Of the 65 documents Florida's investigators have, Mr. Dogali and other lawyers for the ''opt-out'' policyholders, including Michael Malakoff of Pittsburgh and Samuel Wilner of Los Angeles, seem most interested in one. It is identified in an appendix in Judge McClure's April injunction only as ''Coopers & Lybrand assessment of internal controls'' at Prudential Insurance and Financial Services, and dated June 30, 1994. The three lawyers say they believe the document, prepared by the Manhattan-based accounting firm Coopers & Lybrand, is an extensive review of Prudential's sales practices and policies, including interviews with sales agents nationwide.

Although Mr. Dogali said he had never seen the Coopers & Lybrand document, he said he had learned independently that only Prudential's highest executives received copies. The copy that wound up in the Florida Insurance Department came from a locked box at Prudential's headquarters in Newark, he said.

Mr. Malakoff, the Pittsburgh lawyer, said he suspected that the Coopers & Lybrand report might contain the names of some policyholders who were deceived by Prudential sales agents. ''It might show what upper management knew about the sales and when,'' Mr. Malakoff said. ''It might show how people proceeded with the cooperation of the company. It could be a road map for the litigation. I think it would be valuable for everybody.''

Wendy Goldberg, an associate of Mr. Wilner, the Los Angeles lawyer, said they ''assume'' the Coopers & Lybrand document says that Prudential's senior management knew about the improper sales practices and approved them.

She said Mr. Wilner had filed a suit in California courts asking punitive damages for 80 policyholders who claim they were victimized. She also said they have clients in New York, New Jersey, Florida and Illinois.

Prudential has contended in its lawsuits in Florida and New Jersey that the documents were stolen from company offices and given improperly to Florida officials last fall and winter by a high-ranking Prudential executive and lawyer, Renwick T. Nelson. Mr. Nelson helped plan the company's nationwide defense against both policyholder lawsuits and various state investigations of its sales practices, but was dismissed about a month after Florida fined Prudential $15 million, the insurer said.

On March 26, the same day he received Prudential's complaint, a Federal magistrate, Joel A. Pisano, barred Mr. Nelson from discussing the documents with anyone except his lawyer and Prudential. Magistrate Pisano also granted Prudential's request that all material relating to Mr. Nelson in his court be sealed.

On May 23, a Federal judge in Newark, Alfred M. Wolin, broadened the injunction against Mr. Nelson. Judge Wolin approved the class-action settlement last March and is now overseeing its implementation.

He ordered Mr. Nelson to notify Prudential if he was asked to testify in any judicial or government proceeding about Prudential or if investigators from any government agency sought to question him. If questioned under either circumstance, Mr. Nelson was ordered to abide by Prudential's instructions about its attorney-client assertions on the Florida documents.

That order, like Magistrate Pisano's in March, was sealed. The seal was lifted on June 27.

Although Judge Wolin's order seemed to imply that a Government investigation of Prudential was under way, the office of the United States Attorney for New Jersey has refused to comment on whether it or the Federal Bureau of Investigation has begun an inquiry.

Of the 8.5 million Prudential customers who bought about 10.7 million policies from 1982 to 1995 and were eligible to join the class-action settlement, about 2 million asked for applications to participate by a deadline last month, said Mr. DeFillippo, of Prudential. There is no way of knowing now how many people will return the applications. The deadline for returning them is 90 days after receipt.

Mr. Dogali said 19,000 customers had refused to participate in the class action settlement, and a probable 7,000 to 8,000 would actually file lawsuits for punitive damages in either state or Federal courts.

Prudential has acknowledged that some of its sales agents improperly persuaded customers to cash in or borrow against existing policies to buy new and often more expensive ones in a tactic known as churning. Lawyers for policyholders also say that Prudential agents improperly told customers that accumulated dividends in some of the new policies would be sufficient to pay all future premiums after the seventh year of the policy. But, it turned out, the lawyers say, the dividends were not high enough.

After Florida completed its investigation last winter, it turned over some of its most important documents to the Insurance Department in Texas. That state, which initially refused, as Florida did, to accept the class action settlement, ultimately fined Prudential $2 million for deceptive sales practices.

Weeks ago, Texas insurance officials said, lawyers for some policyholders who rejected the settlement, asked Texas, under the state's open-records law, to give them its investigative materials, including the Florida documents.

Prudential has challenged release of the materials.

Texas insurance officials say they balked at the lawyers' request because Judge McClure had said in his April ruling that -- ''to the extent allowed by law'' -- it applied to regulatory agencies in other states.

On July 28, the Texas Attorney General's office prohibited the Insurance Department from releasing the Florida records because of Judge McClure's April ban on disclosure.